CHAPTER 2 The Climate Before the Collapse
We have known for a long time that the climate is changing. Numerous ice ages and warming periods have shown that the Earth's climate is constantly undergoing change. In terms of human lifetimes, each of these periods lasted a relatively long time. In the more recent history of the Earth, ice ages have occurred about every 100 000 years, always interrupted by much shorter warmer periods, referred to as interglacial periods. Our current warm period, called the Holocene era, began about 11 700 years ago. As the previous interglacial periods on average lasted only about 15 000 years, we should be heading towards the next ice age.
The exact causes for the alternation between interglacial periods and ice ages can only be reconstructed to a point. Natural effects, such as changes in solar activity, changes in the geometry of the Earth's orbit, vulcanism, changes in the ocean currents and the shifting of continental plates are considered the main causes of climate change. When multiple causes occur at the same time, very abrupt changes are possible. This is confirmed by the climate history of the Earth. In this sense, the global warming that we have observed in recent years is nothing out of the ordinary. What is unusual, however, is that, for the first time it is apparently living things on Earth – namely, human beings – that are causing an abrupt change in climate.